Low-hysteresis elastomer compositions using amino-substituted aryllithium polymerization initiators

ABSTRACT

A vulcanizable elastomeric compound and products such as pneumatic tires and the like, are formed from a functionalized polymer having a functional group derived from an anionic polymerization initiator. The anionic polymerization initiator comprises the general formula ##STR1## where R 1  -R 5  are the same or different and are selected from the group consisting of hydrogen; alkyls having from alkyls having from 1 to about 12 carbon atoms; aralkyls having from 7 to about 20 carbon atoms; dialkylaminos having from 2 to about 20 carbon atoms; and, dialkylaminoalkyls having from 3 to about 20 carbon atoms. At least one of R 1  -R 5  is selected from the group consisting of the dialkylaminos and the dialkylaminoalkyls. Methods of the present invention include preparing functionalized polymers and reducing the hysteresis of vulcanizable elastomeric compounds.

This application is a division of application Ser. No. 07/814,935, filedDec. 30, 1991, now U.S. Pat. No. 5,274,106.

TECHNICAL FIELD

The subject invention relates to the anionic polymerization of dienepolymer and copolymer elastomers. More specifically, the presentinvention relates to anionic polymerization employing anamino-substituted aryllithium initiator compound.

Diene polymers and copolymers prepared according to the presentinvention, have reduced hysteresis characteristics. Articles such astires, power belts and the like which are prepared from these polymersexhibit increased rebound, decreased rolling resistance and less heatbuild-up during mechanical stress operations.

BACKGROUND OF THE INVENTION

In the art it is desirable to produce elastomeric compounds exhibitingreduced hysteresis. Such elastomers, when compounded to form articlessuch as tires, power belts and the like, will show an increase inrebound, a decreased rolling resistance and will have less heat build-upwhen mechanical stresses are applied.

Previous attempts at preparing reduced hysteresis products have includedhigh temperature mixing of the filler-rubber mixtures in the presence ofselectively-reactive promoters to promote compounding materialreinforcement; surface oxidation of the compounding materials; chemicalmodifications to the terminal end of polymers usingtetramethyldiaminobenzophenone (Michler's ketone), tin coupling agents,aminoaldehydes, tetrachlorofulvenes, various amides and ureas, certaincyclic amides and lactams, dimethylimidazolidinone, carbodiimide,pyridine and the like; and, surface grafting thereon. All of theseapproaches have focused upon increased interaction between the elastomerand the compounding materials.

It has also been recognized that carbon black, employed as a reinforcingfiller in rubber compounds, should be well dispersed throughout therubber in order to improve various physical properties. One example ofthe recognition is provided in published European Pat. Appln. EP 0 316255 A2 which discloses a process for end capping polydienes by reactinga metal terminated polydiene with a capping agent such as a halogenatednitrile, a heterocyclic aromatic nitrogen containing compound or analkyl benzoate. Additionally, that application discloses that both endsof the polydiene chains can be capped with polar groups by utilizingfunctionalized initiators, such as lithium amides.

The present invention provides novel initiators for anionicpolymerization which become incorporated into the polymer chainproviding a functional group which greatly improves the dispersabilityof carbon black throughout the elastomeric composition duringcompounding. As will be described hereinbelow, these initiators arecompounds containing an amino-substituted aryl group.

Organolithium polymerization initiators are also known in the art. U.S.Pat. No. 3,439,049, owned by the Assignee of record, discloses anorganolithium initiator prepared from a halophenol in a hydrocarbonmedium.

U.S. Pat. No. 4,015,061 is directed toward amino-functional initiatorswhich polymerize diene monomers to form mono- or all-primary arylamine-terminated diene polymers upon acid hydrolysis.

U.S. Pat. No. 4,914,147 discloses terminal modifying agents includingdialkylamino-substituted aromatic vinyl compounds such asN,N'-dimethylamino benzophenone and p-dimethylamino styrene, in rubbercompositions having reduced hysteresis characteristics. In U.S. Pat. No.4,894,409, an amino group-containing monomer, such as2-N,N-dimethylaminostyrene is polymerized to form an aminogroup-containing diene based polymer.

Thus, the foregoing art has not employed an amino-substitutedaryllithium initiator compound for the incorporation of anamino-substituted aryl functional group at one end of the chain, with alithium atom at the opposite end prior to quenching.

SUMMARY OF INVENTION

It is therefore an object of the present invention to provide anionicpolymerization initiators which promote the incorporation of functional,active groups in the polymer chain.

It is another object of the present invention to provide a method ofpreparing an anionic polymerization initiator.

It is another object of the present invention to provide functionalizedpolymers having active terminal groups.

It is another object of the present invention to provide a method forpreparing functionalized polymers having active terminal groups.

It is still another object of the present invention is to provide amethod for the preparation of a functionalized polymer.

It is yet another object of the present invention is to provide a methodfor reducing the hysteresis of elastomeric vulcanizable compounds.

It is another object of the present invention to provide vulcanizableelastomeric compounds having reduced hysteresis.

It is still another object of the present invention to provide animproved pneumatic tire having decreased rolling resistance.

These and other objects together with the advantages thereof over theexisting art, which shall become apparent from the specification whichfollows, are accomplished by the invention as hereinafter described andclaimed.

In general the present invention provides an anionic polymerizationinitiator which comprises the general formula ##STR2## where R¹ -R⁵ arethe same or different and are selected from the group consisting ofhydrogen; alkyls having from 1 to about 12 carbon atoms; aralkyls havingfrom 7 to about 20 carbon atoms; dialkylaminos having from 2 to about 20carbon atoms; and, dialkylaminoalkyls having from 3 to about 20 carbonatoms. At least one of R¹ -R⁵ is selected from the group consisting ofthe dialkylaminos and the dialkylaminoalkyls.

There is also provided according to the invention, a functionalizedpolymer which comprises a polymer chain carrying a functional group atone end of the chain and a lithium atom at the other end of the chainprior to quenching. The functional group has the general formula##STR3## where R¹ -R⁵ are the same or different and are selected fromthe group consisting of hydrogen; alkyls having from 1 to about 12carbon atoms; aralkyls having from 7 to about 20 carbon atoms;dialkylaminos having from 2 to about 20 carbon atoms; and,dialkylaminoalkyls having from 3 to about 20 carbon atoms. At least oneof R¹ -R⁵ is selected from the group consisting of the dialkylaminos andthe dialkylaminoalkyls.

There is also provided according to the invention, a functionalizedpolymer of the type formed by the polymerization of at least oneanionically polymerizable monomer, and improved with respect to itshysteresis properties. The improvement comprises polymerizing themonomer in the presence of a polymerization initiator having the generalformula ##STR4## where R¹ -R⁵ are the same or different and are selectedfrom the group consisting of hydrogen; alkyls having from 1 to about 12carbon atoms; aralkyls having from 7 to about 20 carbon atoms;dialkylaminos having from 2 to about 20 carbon atoms; and,dialkylaminoalkyls having from 3 to about 20 carbon atoms. At least oneof R¹ -R⁵ is selected from the group consisting of the dialkylaminos andthe dialkylaminoalkyls.

Further still according to the invention, a vulcanizable elastomericcompound having reduced hysteresis properties, comprises an elastomericpolymer having a plurality of chains. Substantially each chain carries afunctional group at the initiator end of the chain and a lithium atom atthe other end of the chain, prior to quenching. The functional group hasthe general formula ##STR5## where R¹ -R⁵ are the same or different andare selected from the group consisting of hydrogen; alkyls having from 1to about 12 carbon atoms; aralkyls having from 7 to about 20 carbonatoms; dialkylaminos having from 2 to about 20 carbon atoms; and,dialkylaminoalkyls having from 3 to about 20 carbon atoms. At least oneof R¹ -R⁵ is selected front the group consisting of the dialkylaminosand the dialkylaminoalkyls.

An improved tire according to the invention has decreased rollingresistance, and results from a treadstock containing a vulcanizableelastomeric composition which comprises an elastomeric polymer having aplurality of chains. Substantially each chain carries a functional groupat the initiator end of the chain and a lithium atom at the other end ofthe chain prior to quenching. The functional group has the generalformula ##STR6## where R¹ -R⁵ are the same or different and are selectedfrom the group consisting of hydrogen; alkyls having from 1 to about 12carbon atoms; aralkyls having from 7 to about 20 carbon atoms;dialkylaminos having from 2 to about 20 carbon atoms; and,dialkylaminoalkyls having from 3 to about 20 carbon atoms. At least oneof R¹ -R⁵ is selected from the group consisting of the dialkylaminos andthe dialkylaminoalkyls.

The present invention also provides a method of preparing afunctionalized polymer comprising the steps of forming a solution of oneor more anionically polymerizable monomers in a solvent; and,polymerizing the monomers in the presence of a polymerization initiatorhaving the general formula ##STR7## where R¹ -R⁵ are the same ordifferent and are selected frown the group consisting of hydrogen;alkyls having from 1 to about 12 carbon atoms; aralkyls having from 7 toabout 20 carbon atoms; dialkylaminos having from 2 to about 20 carbonatoms; and, dialkylaminoalkyls having from 3 to about 20 carbon atoms;and where at least one of R¹ -R⁵ is selected from the group consistingof the dialkylaminos and the dialkylaminoalkyls.

Finally, a method for reducing the hysteresis of vulcanizableelastomeric compounds is provided which comprises the steps ofpolymerizing one or more anionically polymerizable monomers in thepresence of an initiator having the general formula ##STR8## where R¹-R⁵ are the same or different and are selected from the group consistingof hydrogen; alkyls having from 1 to about 12 carbon atoms; aralkylshaving from 7 to about 20 carbon atoms; dialkylaminos having from 2 toabout 20 carbon atoms; and, dialkylaminoalkyls having from 3 to about 20carbon atoms; and where at least one of R¹ -R⁵ is selected from thegroup consisting of the dialkylaminos and the dialkylaminoalkyls;quenching the polymerization to form an elastomer; and adding from about5 to 80 parts by weight of carbon black, per 100 parts of the elastomerto form a blend of the vulcanizable elastomeric composition.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

As will become apparent from the description which follows, the presentinvention provides a novel initiator for anionic polymerization of dienehomopolymer and copolymer elastomers. Polymers prepared with theseinitiators contain a functional terminal group, and it has beendiscovered herein that vulcanizable elastomeric compounds and articlesthereof based upon such functionally terminated polymers exhibit usefulproperties, particularly, reduced hysteresis. When compounded to makeproducts such as tires, power belts and the like, these polymericproducts exhibit increased rebound, decreased rolling resistance andless heat build-up during periods of applied mechanical stress.

The initiators according to the present invention are amino-substitutedaryllithium compounds. More particularly, the initiators according tothe present invention have the following general formula ##STR9## Thegroups R¹, R², R³, R⁴ and R⁵ (collectively referred to herein as "R¹ -R⁵") may be the same or different. Each of the groups R¹ -R⁵ may be ahydrogen; an alkyl having from 1 to about 12 carbon atoms; an aralkylhaving from 7 to about 20 carbon atoms; a dialkylamino having from 2 toabout 20 carbon atoms; or a dialkylaminoalkyl having from 3 to about 20carbon atoms. At least one of the groups R¹ -R⁵ is either one of thedialkylaminos or the dialkylaminoalkyls.

The initiators according to the present invention are for example, theproducts of ring-metalation of amino aryl compounds; or metal-halogenexchange reactions with aminoaryl halides; or, the reduction ofaminoarylhalides with lithium.

One preferred initiator is formed by the reaction of n-butyl lithium orsec-butyl lithium, with the reaction product ofN',N"-dimethylethylenediamine and 4-(N,N-diethylamino) benzaldehyde.This initiator compound, hereinafter designated as "structure I" has theformula ##STR10##

Another preferred initiator is a tetramethyl-p-phenylene diamine,hereinafter designated as "structure II", and which has the formula##STR11##

Still another preferred initiator is the metal-halogen exchange productof the cyclic aminal of N,N'-dimethyl ethylenediamine and4-bromobenzaldehyde, hereinafter designated as "structure III" and whichhas the formula ##STR12##

Other suitable initiators may be formed for example, by the reduction ofother aminoaryl bromides with lithium metal, or by exchange withalkyllithium compounds.

The initiator thus prepared, is employed to prepare anyanionically-polymerized elastomer, e.g., polybutadiene, polyisoprene andthe like, and copolymers thereof with monovinyl aromatics such asstyrene, alpha methyl styrene and the like, or trienes such as myrcene.Thus, the elastomers include diene homopolymers, A, and copolymersthereof with monovinyl aromatic polymers, B. Exemplary dienehomopolymers are those prepared from diolefin monomers having from 4 toabout 12 carbon atoms. Exemplary vinyl aromatic polymers are thoseprepared from monomers having from 8 to about 20 carbon atoms. Preferredelastomers include diene homopolymers such as polybutadiene andpolyisoprene and copolymers such as styrene butadiene rubber (SBR).Copolymers can comprise from about 99 to 20 percent by weight of dieneunits and from about 1 to about 80 percent by weight of monovinylaromatic or triene units, totalling 100 percent. The polymers andcopolymers of the present invention may have 1,2-microstructure contentsranging from about 10 to about 80 percent, with the preferred polymersor copolymers having 1,2-microstructure contents of from about 25 to 65percent, based upon the diene content. The molecular weight of thepolymer that is produced according to the present invention, ispreferably such that a proton-quenched sample will exhibit a gum Mooneyviscosity (ML/4/22) of from about 10 to about 150.

The copolymers are preferably random copolymers which result fromsimultaneous copolymerization of the monomers forming the A and Bpolymer blocks, as is known in the art. The block copolymers (poly(b-B-b-A-b-B)), result from the separate polymerization of the monomersforming the A and B polymer blocks as is known in the art. Such blockcopolymers which include poly(styrene-butadiene-styrene) arethermoplastic elastomers.

The initiators of the present invention form "living polymers" from theforegoing monomers, the general formula prior to quenching of which is

    R.sup.6 --polymer--Li

where the polymer is any of the foregoing diene homopolymers, monovinylaromatic homopolymers, diene/monovinyl aromatic random copolymers andblock copolymers and R⁶ is a functional group derived from theinitiator. R⁶ is preferably ##STR13## where R¹ -R⁵ are as definedhereinabove. The lithium proceeds to move down the growing chain aspolymerization continues, until the reaction is quenched.

Polymerization is usually conducted in a conventional solvent foranionic polymerizations such as hexane, cyclohexane, benzene and thelike. Other techniques for polymerization, such as semi-batch andcontinuous polymerization may be employed. In order to promoterandomization in copolymerization and to increase vinyl content, amodifier may optionally be added to the polymerization ingredients.Amounts range between 0 to 90 or more equivalents per equivalent oflithium. The amount depends upon the amount of vinyl desired, the levelof styrene employed and the temperature of the polymerizations, as wellas the selected modifier.

Compounds useful as modifiers are organic and include those having anoxygen or nitrogen hetero-atom and a non-bonded pair of electrons.Examples include dialkyl ethers of mono and oligo alkylene glycols;"crown" ethers; tertiary amines such as tetramethylethylene diamine(TMEDA); THF; THF oligomers; linear and cyclic oligomeric oxolanylalkanes, and the like. Details of linear oligomeric oxolanyl modifierscan be found in U.S. Pat. No. 4,429,091, owned by the Assignee ofrecord, the subject matter of which is incorporated herein by reference.

Polymerization is usually begun by charging a blend of the monomer(s)and solvent to a suitable reaction vessel, followed by the addition ofthe modifier and the initiator solution previously described.Alternatively, the monomer and modifier can be added to the initiator.The procedure is carried out under anhydrous, anaerobic conditions. Thereactants are heated to a temperature of from about 30° to 120° C. andare agitated for about 0.15 to 24 hours. After polymerization iscomplete, the product is removed from the heat and terminated in one ormore ways.

For example, a protic quenching agent may be employed to give amonofunctional polymer chain. Quenching may be conducted in water, steamor an alcohol such as isopropanol, or any other suitable method.Quenching may also be conducted with a functional terminating agent,resulting in a difunctional polymer. For example, useful functionalterminating agents include alkenyl aromatic vinyl compounds, halogenatedtin compounds such as tributyl tin chloride and tin tetrachloride,halogenated silicon compounds, isocyanate compounds,dialkylamino-substituted aromatic vinyl compounds, nitrogen-containingaromatic hetero compounds, cyclic urea, and other reactivehysteresis-reducing terminating compounds which may contain otherheteroatoms such as oxygen, nitrogen, sulfur, phosphorus,non-interfering halogen, or the like. Other terminators include isomericvinylpyridines, dimethylimidazolidinone, Schiff bases and the like. Theliving polymer may also be coupled with any of the known couplingreagents such as silicon tetrachloride, to prepare dicapped polymers.

Further examples of terminating agents include the terminators describedin copending application Ser. No. 07/506,305, now U.S. Pat. No.5,153,159 and U.S. Pat. No. 5,066,729, the subject matter of which isincorporated by reference herein. It is to be understood that practiceof the present invention is not limited solely to these terminatorsinasmuch as other compounds that are reactive with the polymer boundcarbon-lithium moiety can be selected to provide a desired functionalgroup.

Quenching is usually conducted by stirring the polymer and quenchingagent for about 0.05 to about 2 hours at temperatures of from about 30°to 120° C. to ensure complete reaction. Polymers terminated with afunctional group as discussed hereinabove, are subsequently quenchedwith alcohol or other quenching agent as described hereinabove.

Lastly, the solvent is removed from the polymer by drum drying, extruderdrying, vacuum drying or the like, which may be combined withcoagulation with water, alcohol or steam. If coagulation with water orsteam is used, oven drying may be desirable.

The polymers of the present invention contain a functional group at thehead of the polymer chain rather than at the terminal end of the chain.These functional groups have an affinity for compounding materials suchas silica and carbon black. Such compounding results in productsexhibiting reduced hysteresis, which means a product having increasedrebound, decreased rolling resistance and has lessened heat build-upwhen subjected to mechanical stress. Products including tires, powerbelts and the like are envisioned. Decreased rolling resistance is, ofcourse, a useful property for pneumatic tires, both radial as well asbias ply types and thus, the vulcanizable elastomeric compositions ofthe present invention can be utilized to form treadstocks for suchtires.

The polymers of the present invention can be utilized as 100 parts ofthe rubber in the treadstock compound or, they can be blended with anyconventionally employed treadstock rubber which includes natural rubber,synthetic rubber and blends thereof. When the polymers of the presentinvention are blended with conventional rubbers, the amounts can varywidely with a lower limit comprising about 10 to 20 percent by weight ofthe total rubber. It is to be appreciated that the minimum amount willdepend primarily upon the degree of reduced hysteresis that is desired.

The polymers can be compounded with all forms of carbon black in amountsranging from about 5 to 80 parts by weight, per 100 parts of rubber(phr), with about 35 to 60 phr being preferred. The carbon blacks mayinclude any of the commonly available, commercially-produced carbonblacks but those having a surface area (EMSA) of at least 20 m² /gramand more preferably at least 35 m² /gram up to 200 m² /gram or higherare preferred. Surface area values used in this application are thosedetermined by ASTM test D-1765 using the cetyltrimethyl-ammonium bromide(CTAB) technique. Among the useful carbon blacks are furnace black,channel blacks and lamp blacks. More specifically, examples of thecarbon blacks include super abrasion furnace (SAF) blacks, high abrasionfurnace (HAF) blacks, fast extrusion furnace (FEF) blacks, fine furnace(FF) blacks, intermediate super abrasion furnace (ISAF) blacks,semi-reinforcing furnace (SRF) blacks, medium processing channel blacks,hard processing channel blacks and conducting channel blacks. Othercarbon blacks which may be utilized include acetylene blacks. Mixturesof two or more of the above blacks can be used in preparing the carbonblack products of the invention. Typical values for surface areas ofusable carbon blacks are summarized in the TABLE I hereinbelow.

                  TABLE I                                                         ______________________________________                                        Carbon Blacks                                                                 ASTM           Surface Area                                                   Designation    (m.sup.2 /g)                                                   (D-1765-82a)   (D-3765)                                                       ______________________________________                                        N-110          126                                                            N-220          111                                                            N-339          95                                                             N-330          83                                                             N-351          74                                                             N-550          42                                                             N-660          35                                                             ______________________________________                                    

The carbon blacks utilized in the preparation of the rubber compounds ofthe invention may be in pelletized form or an unpelletized flocculentmass. Preferably, for more uniform mixing, unpelletized carbon black ispreferred.

The reinforced rubber compounds can be cured in a conventional mannerwith known vulcanizing agents at about 0.1 to 10 phr. For a generaldisclosure of suitable vulcanizing agents one can refer to Kirk-Othmer,Encyclopedia of Chemical Technology, 3rd ed., Wiley Interscience, N.Y.1982, Vol. 20, pp. 365-468, particularly "Vulcanization Agents andAuxiliary Materials" pp. 390-402. Vulcanizing agents can be used aloneor in combination.

Vulcanizable elastomeric compositions of the invention can be preparedby compounding or mixing the functionalized polymers herein with carbonblack and other conventional rubber additives including for example,fillers, such as silica, plasticizers, antioxidants, curing agents andthe like using standard rubber mixing equipment and procedures. Suchelastomeric compositions when vulcanized using conventional rubbervulcanization conditions have reduced hysteresis properties and areparticularly adapted for use as tread rubbers for tires having reducedrolling resistance.

General Experimental

In order to demonstrate the preparation and properties of elastomersprepared according to the present invention, several initiators wereprepared according to the disclosure made hereinabove. The initiatorswere used to polymerize a styrene butadiene rubber (SBR). As notedabove, various techniques known in the art for carrying outpolymerizations may be used with these initiators without departing fromthe scope of the present invention.

EXAMPLE NO. 1 Preparation of Polymer from Initiator I

Preparation of Initiator

The cyclic aminal precursor of structure I was prepared by thecondensation of equimolecular amounts of N,N'-dimethylethylene diaminewith p-diethylaminobenzaldehyde, carried out in refluxing toluene withcontinuous azeotropic removal of water. The product distilled at123°-125° C. at 1 Torr, and was found to be of 96+ percent purity byGC/MS. The ortho-Li derivative was prepared by treating the cyclicaminal with 1.0 equivalent of sec-butyl Li and 0.8 equivalent oftetramethylethylene diamine (TMEDA) for 16 hours at 50° C. in ahexane/cyclohexane solution. The resulting solution was approximately0.57 molar, and was used to intitiate polymerization.

Polymerization of Butadiene and Styrene

A 0.57M solution of an initiator made in the above manner was added to a75 percent/25 percent by weight blend of butadiene and styrene inhexane, at a level of 0.8 meq Li/100 g monomer. The mixture was agitatedat 50° C. for 4.5 hours, proceeding to approximately 100 percentconversion to polymer. In practice, there is considerable leeway in thereaction times and temperatures, much the same as there is leeway in thereaction vessels, type of agitation, etc., used. The treated cementsthen were quenched by injection with 1.5 ml of isopropyl alcohol(i-PrOH), treated with an antioxidant (2 ml of a mixture containing 2.0weight percent DBPC/and 0.07 weight percent UOP-88 in hexane),coagulated in i-PrOH, air-dried at room temperature, then drum-dried.Suitable characterizations were performed. The product polymer contained25.4 percent styrene (2.8 percent block); 30.4 percent vinyl (42 percentvinyl if BD=100 percent), Tg-27.1° C., GPC(THF):Mn 147748, MWD 1.66, rawML/4/100=54.

Evaluation of Compounded Properties

The product polymer was compounded and tested as indicated in the testrecipe shown in Table I, and cured according to the following:1.5"×4"×0.040" tensile plaques, 35 minutes at 300° F.; Dynastat buttons,40 minutes at 300° F.

                  TABLE II                                                        ______________________________________                                        Compound Formulation for Evaluation of Hysteresis                             Component        Parts per Hundred Parts Rubber                               ______________________________________                                        Polymer          100                                                          Naphthenic Oil   10                                                           Carbon Black, N-351                                                                            55                                                           ZnO              3                                                            Antioxidant      1                                                            Wax Blend        2                                                            Total Masterbatch                                                                              171                                                          Masterbatch mixed for 5 min-                                                  utes at 145° to 155° C., 60 RPM                                 Stearic Acid     2                                                            Sulfur           1.5                                                          Accelerator      1                                                            Total Final      175.5                                                        Final mix at 77° to 93° C.,                                     40 RPM, for 3 minutes                                                         ______________________________________                                    

Results of physical tests were as follows:

    ______________________________________                                                            1 Hz Dynastat                                             Example No.                                                                            ML/4/212   tan δ Ring Stress-Strain                            ______________________________________                                                                50° C.                                                                           Room Temp.                                           (gum)   (cpd)            M300 T.S. % Eb                              1        54      83     0.1037    2251.sup.a 2996.sup.a                       ______________________________________                                                                          442                                          .sup.a psi                                                               

The results of this test provided good evidence for reduced hysteresisin this polymer. The Dynastat tan δ(50° C.)=0.1037. is about 30 percentbelow the value found for an unmodified polymer of this molecularweight, prepared using a typical alkyllithium initiator.

EXAMPLE NO. 2 Preparation and Evaluation of Polymer from Initiator II

Tetramethyl-p-phenylenediamine was treated with s-BuLi/TMEDA incyclohexane in a manner similar to that described above. It initiatedpolymerization to give SBR with 26.1 percent styrene (0 percent block),47.8 percent vinyl, Tg -23.6° C., Mn 150148, Mw/Mn 1.62. When tested inthe standard recipe using the Dynastat, the compounded polymer had tanδ(50° C.)=0.1323, which is about 10 percent below the value expected foran unmodified polymer of this molecular weight, prepared using a typicalalkyllithium initiator.

EXAMPLE NO. 3 Preparation of Polymer from Initiator III

The cyclic aminal of p-bromobenzaldehyde was prepared in a mannersimilar to that for the precursor of I: A 10 mole percent excess ofN,N'-dimethylethylene diamine was refluxed in the presence ofp-bromobenzaldehyde in toluene for three days, with azeotropic removalof water. After removal of solvent by distillation, the residue wasdistilled under vacuum, to give the cyclic aminal in 96 percent yield.The structure of the product was confirmed by ¹ HNMR (CDCl₃); δ2.13(s,6H), 2.49 (m, 2H); 3.21 (s, 1H); 3.40 (m, 2H); 7.42 (m, 4H) (noabsorption below 7.5δ). It was readily soluble in hexane. Upon treatmentof a hexane solution of this aminal with an equimolar amount of n-BuLiin hexane, a precipitate formed.

This heterogeneous initiator was used in the following manner topolymerize a mixture of butadiene and styrene: A dried, nitrogen purgedbottle was closed with a crown seal containing a rubber liner, andcharged by needle through the liner with 427.0 grams of a 25 percent byweight solution of a 75/25 (w/w) blend of butadiene and styrene inhexane. A 0.5M hexane solution of a linear oligomeric oxolanyl ether wasthen charged by needle, such that 0.15 mole of ether per mole of Li waspresent, and then 2.59 ml of a 0.33M (heterogeneous) mixture of the p-Liphenyl aminal (III) was charged (about 0.8 meq Li per hundred grams ofmonomer). The bottle was agitated for 16 hours at 80° C., and thenallowed to cool, and the contents were worked up as indicated in ExampleI. The product polymer was recovered in 54 percent yield and contained15.4 percent styrene (0 percent block styrene), 28.4 percent vinyl (33.6percent vinyl if butadiene=100 percent), Tg=-65° C. (DSC, onset), GPC(THF): Mn 104471, Mw/Mn 2.31. The product polymer was compounded andtested as outlined in Example I.

The results of the physical tests were as follows:

    ______________________________________                                                           1 Hz Dynastat                                              Example No.                                                                             ML/4/212 tan δ Ring Stress-Strain                             ______________________________________                                                  (cpd)    50° C.                                                                         23° C.                                                                       Room Temp.                                                                    M300 T.S. % Eb                               3         76       0.1361  0.1549                                                                              1972.sup.a 2952.sup.a 459                    ______________________________________                                         .sup.a psi                                                               

The results of this test showed evidence for reduced hysteresis in thispolymer, in that the Dynastat tan δ (50° C.)=0.1361 is about 30 percentbelow the value found for an unmodified polymer of this molecularweight, prepared using a typical alkyllithium initiator. Two other SBRpolymers prepared in a similar manner using the lithium salt derivedfrom the cyclic aminal of p-bromobenzaldehyde, and compounded andevaluated in the same way, exhibited tan δ (50° C.) which were 34percent and 20 percent lower than the values expected for unmodified SBRpolymers of their molecular weights.

In conclusion, it should be clear from the foregoing examples andspecification disclosure that the initiators of the present inventionare useful for the anionic polymerization of diene monomers to formhomopolymers as well as copolymers with monovinyl aromatic monomers ortrienes. The resulting elastomeric polymers have a functional group atthe site of initiation and a lithium atom at the terminal, "living" end.After quenching, the polymers still retain the functional group at thesite of initiation, which promotes uniform and homogeneous mixing withcarbon black. As a result vulcanizable elastomeric compounds containingthese polymers exhibit improved hysteresis which provides lower rollingresistance in tires and improved fuel economy. Additionally, the lithiumterminated polymers can be quenched with compounds to provide terminalfunctional groups and hence, difunctional polymer chains.

It is to be understood that the invention is not limited to the specificreactants, initiators, or other compounds disclosed nor to anyparticular modifier or solvent. Similarly, the examples have beenprovided merely to demonstrate practice of the subject invention and donot constitute limitations of the invention. Those skilled in the artmay readily select other monomers and process conditions, according tothe disclosure made hereinabove.

Thus, it is believed that any of the variables disclosed herein canreadily be determined and controlled without departing from the scope ofthe invention herein disclosed and described. Moreover, the scope of theinvention shall include all modifications and variations that fallwithin the scope of the attached claims.

What is claimed is:
 1. A vulcanizable elastomeric composition havingreduced hysteresis properties, comprising:an elastomeric polymer havinga plurality of chains and selected from the group consisting of dienehomopolymers and copolymers with monovinyl aromatic polymers;substantially each said chain carrying a functional group at theinitiator end of said chain and a lithium atom at the other end of saidchain prior to quenching, and having the general formula:

    R.sup.6 --polymer--Li

wherein R⁶ is a functional group having a structure selected from thegroup consisting of ##STR14## and, from about 5 to 80 parts by weight ofcarbon black, per 100 parts of said elastomeric polymer.
 2. Avulcanizable elastomeric composition as set forth in claim 1, whereinsaid elastomeric polymer is prepared from monomers selected from thegroup consisting of diolefins having from about 4 to about 12 carbonatoms, monovinyl aromatic monomers having from 8 to about 20 carbonatoms, and trienes.
 3. A vulcanizable elastomeric composition, as setforth in claim 2, wherein said monomers are butadiene and styrene.